Why does my Lumia 1520 lags for 2 to 3 secs when coming to lock screen?

My Lumia 1520 has slowed down since few days when it's coming to lock screen from the sleep mode. It says "Resuming" before it reaches the lock screen for me to swipe up and tap the code to unclock. Anybody facing the same issue?? I have deleted temporary memory and deleted history on IE as well. Please suggest. Inspite of havinf 2 Gigs of RAM.